Spectroscopic Determinations of Excited State Properties of Organometallic and Inorganic Compounds

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The Inorganic, Bioinorganic and Organometallic Chemistry Program supports basic research in inorganic photochemistry. This project is at the forefront of an area with the potential to benefit society in numerous ways: catalysis, optical and electro-optical devices and photoconversion of energy. The proposed research program is a three-fold investigation of the electronic excited states of organometallic compounds, especially metal carbene, carbyne, olefin and nitrosyl compounds. The first group of experiments is the assignment of excited states by using single crystal polarized spectroscopy. New experimental techniques make it possible to measure absorption bands with high extinction coefficients of oriented molecules in crystals at low temperatures. Detailed assignments will be made. Vibronic structure, when present, will be used to determine the excited state distortions. An additional result is the quantitative experimental measurement of metal-ligand sigma and pi interactions which will be compared with both ligand field and molecular orbital theory. The second component of the program is the determination of excited state distortions by using a combination of pre-resonance Raman spectra, electronic spectra and time-dependent theory. This combination makes it possible to calculate the magnitudes of all of the distortions along normal modes in the excited state potential hypersurface. The third group of experiments is the measurement of geometries of molecules in excited electronic states by using excited state pump-probe Raman spectroscopy. In these experiments, excited states are produced by absorption of one photon and the vibrational spectrum of the molecule in this excited state is measured by Raman spectroscopy with a second photon. This method is complementary to the above techniques and will be especially useful for studying extremely large distortions and metastable intermediates. The goal of the three groups of experiments is the unified understanding of excited state obital characteristics, potential surface displacements, and excited state geometries of organometallics.